A. Field of the Invention
This invention relates generally to medical instruments that have extracorporeal blood circuits, such as hemodialysis machines. More particularly, the invention relates to methods for testing the integrity of such circuits in advance of a treatment session so as to improve patient safety and reliable operation of the machine.
B. Description of Related Art
Various types of medical instruments, most notably artificial kidney and liver dialysis machines, incorporate extracorporeal circuits. The purpose of such extracorporeal circuits is generally to carry the blood from the patient, filter the blood, and return the blood to the patient. Most configurations of the extracorporeal circuit include a line designated "arterial" that connects to a fistula needle inserted into the patient's body. A blood pump segment is placed in the arterial line which, in conjunction with a blood pump in the instrument, pumps blood from the patient's body to a filtration apparatus. The filtration device is a dialyzer in the case of the artificial kidney machine. Blood is then returned to the patient by a second line, termed the "venous" line. Typically, clamps, bubble traps, pressure transducers, injection sites, and other components are included in the arterial or venous line, and serve various functions incident to operation of the machine and/or for purposes of patient safety.
To perform dialysis, the patient connects their arterial and venous fistula needles, or central venous catheters, to connectors terminating the arterial and venous lines of the extracorporeal circuit. When the dialysis session in completed, the patient disconnects the arterial and venous lines from the blood access devices. In some machines, the entire extracorporeal circuit is replaced with a new one for the next session with the machine. In other situations, the extracorporeal circuit is reused. In this latter situation, typically the arterial and venous line connectors are connected either to a disinfection manifold in fluid communication with a source of disinfection fluids, or to a separate reuse device, and the entire extracorporeal circuit is subject to cleaning and disinfection. See e.g., the patent to Kenley et al., U.S. Pat. No. 5,591,344, the patent to Boag, U.S. Pat. No. 4,695,385, and the German patent to Polaschegg, No. DE 3,442,744.
When the extracorporeal circuit is replaced after every use, there is generally less of a concern that the extracorporeal circuit may be defective, since quality assurance testing would generally be performed as an incident to manufacture of the extracorporeal circuit. However, in the case of reuse of the extracorporeal circuit, the need for subsequent integrity testing of the dialyzer and blood tubing set is more pronounced. This is because intervening processes involving the extracorporeal circuit, including the dialysis session, priming, cleaning, disinfection and so forth, present at least a small possibility that the condition of the extracorporeal circuit has been degraded from the condition it was in when it was new.
It is known in the art to test the condition of the dialyzer membrane prior to initiation of dialysis. Procedures for testing the integrity of the dialyzer membrane are described in the above-referenced Kenley et al. and Polaschegg patents, the U.S. Pat. No. 4,834,888 to Polaschegg; U.S. Pat. No. 4,449,392 to Huschke; U.S. Pat. No. 4,444,597 to Gortz, and in the article of W. Gentles et al., Programmable Machine for Dialyzer Reuse, Med. & Bio. Eng. & Comp., Vol. 18, pp. 765-781 (1980). Such tests include pressure tests for detecting leaks in the dialyzer membrane, and clearance tests for determining the capacity of the dialyzer membrane to remove toxins such as urea from the blood.
The present inventors have appreciated that testing the integrity of the dialyzer membrane in the manner known in the prior art overlooks other potential points of failure in the extracorporeal circuit. The inventors have devised methods for in situ testing the remainder of the extracorporeal circuit, including the clamps in the instrument which occlude the arterial and venous lines, the connectors at the end of the lines, adhesion points between the tubing and various rigid connectors, and the tubing itself.
Additionally, the inventors have appreciated that the connection of the arterial and venous line connectors to the disinfection manifold or reuse device is another point of potential failure during disinfection and cleaning operations. The inventors have developed methods for determining whether the arterial and venous lines have been installed on the proper ports of the disinfection manifold or reuse device (i.e., the arterial connector was installed in the "arterial port" and the venous line on the "venous port"). The inventors have also developed methods to determine that the connection is in fact a secure and tight connection such that leakage of fluid or air will not occur when disinfection, priming, and/or cleaning fluids are circulated through the ports, or when integrity testing as described herein is performed.
The result of these achievements is that patient safety and machine operations are both improved. The methods can be performed both on new extracorporeal circuits (i.e., before they are used for the first time in the machine), adding an additional measure of quality assurance, as well as on extracorporeal circuits that are subject to repeated reuse. Further, the advancements provided by the present invention are all the more noteworthy with the advent of dialysis therapy being performed outside of the conventional dialysis clinic environment, and with the more widespread acceptance of dialyzer reuse. In such applications, the integrity testing provided by the present invention gives extra measures of safety and assurances that treatments involving reusable extracorporeal blood circuits can be safely performed outside of conventional dialysis clinic and hospital settings, and in particular in the home, nursing home, and self-care clinic environments.